Carbochlorination processes are utilized in the purification of metal oxide containing ores to produce commercially desirable metals and metal compounds, such as aluminum, zirconium and titanium metals and metal compounds.
In the commercial processes utilizing such carbochlorination processes, a metal oxide bearing ore is chlorinated in the presence of a carbonaceous material as a reducing agent. The carbonaceous materials, typically coke, contain sulfur, which is consumed in the chlorination step. The chlorinator is operated under reducing conditions in order to chlorinate the metal oxide in the ore to form a metal chloride. As a result, the sulfur ends up as a reduced sulfur species, predominantly carbonyl sulfide (carbon oxysulfide) (COS). Accordingly, the gas mixture leaving the reactor contains the metal chlorides, coke, unreacted ore, silicon dioxide, carbon dioxide, carbon monoxide, nitrogen, hydrogen chloride and carbonyl sulfide.
Removal of sulfur from exhaust gases is one of the most important environmental tasks facing industrial manufacturers. Moreover, carbonyl sulfide is difficult to scrub and any venting of the carbonyl sulfide to the atmosphere could count against a production plant's permitted emissions. Alternatively, the sulfur compounds can be oxidized in a thermal oxidizer to form sulfur dioxide (SO2) and scrubbed with sodium hydroxide, a very expensive neutralizer. Accordingly, manufactures utilizing carbochlorination processes have often resorted to utilizing cokes having a low sulfur content rather than less expensive higher sulfur containing cokes in order to minimize the cost of having to deal with carbonyl sulfide.